This invention relates to prosthetic heart valves of the kind that can be collapsed to a reduced circumferential size for delivery to the valve-implant site in a patient (e.g., in or through the lumen of tubular delivery apparatus such as a catheter, a trocar, laparoscopic apparatus, or the like). When the valve is at the implant site, it can be released from the delivery apparatus, which allows the valve to re-expand (or to be re-expanded) to its larger, full, operational, circumferential size. This re-expansion may be wholly elastic, wholly plastic, or partly elastic and partly plastic. Elastic re-expansion may be achieved by using a springy metal such as nitinol in the valve. Plastic expansion may be achieved, for example, by inflating a balloon inside the valve. In addition to restoring the valve to the size that permits it to operate as a valve (i.e., a size at which the flexible leaflets in the valve can open and close), re-expansion of the valve causes the valve to engage native tissue of the patient at the implant site, thereby anchoring the valve at that location in the patient.
Terms like retrieval, repositioning, and removal refer to the ability to return the valve to the delivery apparatus after it has wholly or partly left that apparatus. Such retrieval may be done to allow the valve to be moved to another, different location or orientation in the patient (so-called repositioning), or to completely remove the valve from the patient (so-called removal). Returning the valve to the delivery apparatus involves re-collapsing the valve to its reduced circumferential size. If the valve is to be repositioned, then when the valve is at the desired new location or orientation in the patient, the valve leaves the delivery apparatus again, and it again expands (or is expanded) to its full operating size.
There are many considerations involved in designing a prosthetic heart valve that can collapse to a relatively small diameter without, for example, damaging the flexible leaflets of the valve, and that can also be re-collapsed (e.g., for repositioning) after expansion or partial expansion at the implant site in the patient. There is therefore an on-going need for improvements in these and other areas of prosthetic heart valve design.